Manufacturing and assembly plants, as well as machine shops and garages, often require heavy objects to be lifted, moved to a new location, and released. Many types of hoists have been developed to facilitate the lifting of objects too heavy for humans to lift safely or comfortably without assistance. One particularly useful type of hoist is known as an air balancing hoist. Several versions of air balancing hoists are available. All use air pressure to operate the hoist. Typically, an air balancing hoist includes a housing with an air pressure responsive member movable therein. A cable is connected to the air pressure responsive member such that movement of the air pressure responsive member causes extension or retraction of the cable from the housing. The end of the cable extending from the housing is connected to an object to be lifted and then pressurized air is introduced into the hoist housing. When the air pressure inside the housing reaches a certain level, the air pressure responsive member begins to move and retract the cable toward the housing so that the object connected to the cable is lifted. By controlling the amount of pressure inside the housing, the weight of the object to be lifted can be "balanced" so that the object can be easily moved to another location. When the object to be moved has been positioned at its destination, air pressure in the hoist housing is bled off causing the air pressure responsive member to move and extend the cable, releasing the load.
Under some circumstances, the object to be moved may be released suddenly from the end of the hoist cable without pressure first being removed from the housing. In these circumstances, the weight of the load is no longer available to balance with the air pressure inside of the hoist housing. Therefore, the air pressure responsive member moves very rapidly causing the cable to be retracted very quickly into the housing. This sudden, rapid retraction of the cable is undesirable for several reasons. Rapid retraction of the cable may cause the cable end to whip around in a dangerous manner. Also, the hoist operator may not want the end of the cable to retract entirely into the housing. The operator may wish to lift another object at a similar height to which the first object was released. If the end of the cable is retracted rapidly, the operator must re-extend the cable before the hoist is in a position to be used again. Also, rapid, lengthy travel of the cable and the air responsive member leads to additional wear and tear on the hoist.
There have been numerous attempts to provide cable retraction speed limiters to solve the problem of sudden rapid cable retraction. However, these prior approaches typically rely on some type of brake and are large and complicated. This makes it difficult to package the devices and also increases their costs. There remains a need for a simple and compact cable retraction speed limiter which may be incorporated into new air balancing hoists or retrofitted onto existing air balancing hoists.